The concept of using growth inhibitory or antibacterial susceptibility patterns for bacterial identification is not entirely new. In 1971 Gilardi (Gilardi, G. L., 1971; Appl. Microbiol. 22:821-823) found that susceptibility profiles could be used to assist in the identification of lactose-nonfermenting, gram-negative bacteria. He used susceptibility information, for 16 antibiotics, obtained from the disk agar diffusion method. Sutter and Finegold (Sutter, V. L., and S. M. Finegold, 1971; Appl. Microbiol. 21:13-20) used susceptibility profiles to place gram-negative anaerobic bacilli into five different groups. Further testing was then required to complete the identification.
A Baysean mathematical model was used by Friedman and MacLowry (Friedman, R., and J. MacLowry, 1973; Appln. Microbiol. 26:314-317) to classify bacteria. Their data base contained probability data on the susceptibility profiles of 31 species of bacteria. This data was collected over a period of several years. When 1,000 clinical isolates were classified by this method, there was an 86% agreement with the identification obtained by conventional biochemical procedures.
U.S. Pat. No. 3,832,532 describes a method and apparatus for testing antibiotic susceptibility in conjunction with a determination of the light scatter index (LSI) of the bacteria being tested. Auxiliary methods and equipment for use in such determinations are described in the following U.S. Pat. Nos.: 3,832,532, 3,895,661; 3,899,011; 3,901,588; 3,934,753; 3,942,899; and U.S. Pat. No. De. 230,587. The equipment described in the aforementioned system combines the speed of automation with the flexibility of manual procedures. It is designed to determine the susceptbility of a bacteria to a panel of up to 12 antimicrobial agents simultaneously. The result for each antimicrobial is an index of susceptibility called the "light scatter index" (LSI). The index runs from 0.00 (resistant) to 1.00 (susceptible) in increments of 0.01. The test results, except for certain slow-growing organisms, are available within 3 to 5 hours after the test is begun. An object of this invention is to provide a method and apparatus and suitable identifying agents for use in identifying bacteria in accordance with a determination of LSI values of sample solutions reacted with the agents.